The most notable reform Mr. Obama announced scales back the federal program that provides surplus military-grade equipment to state and local law enforcement agencies. This is the scheme that resulted in grenade launchers and armored vehicles going to school district police, among other absurdities. “We’ve seen how militarized gear can sometimes give people a feeling like there’s an occupying force,” Mr. Obama said Monday. “It can alienate and intimidate local residents, and send the wrong message.”

The president won’t eliminate the program, which was congressionally authorized. Rather, he will ban the transfer of grenade launchers, tracked armored vehicles, weaponized aircraft and bayonets — bayonets! — to police departments. Other military materiel, such as plain old armored vehicles and riot gear, will still be eligible for transfer. But police departments will have to explain why they need such items, and the equipment will come with new strings attached, such as a requirement to report on how it is used.

Though the federal government doesn’t have direct control over state and local police, it can do more to encourage better policing. The president’s Task Force on 21st Century Policing detailed some straightforward ways Monday. Encouraging better collection and use of data is particularly urgent. If police departments can discern early warning signs in the recorded activities of problem officers, for example, they can be retrained or reassigned before they make major mistakes.

Along with encouraging better use of data, the administration is investing in police body cameras. At least as important as encouraging the development and deployment of the technology, though, will be working through difficult privacy issues about what sort of body camera footage can be made public, and when, not to mention how long the information should be stored. The Justice Department can be a force for intelligent accountability as standards are set.

Congress has a role, too. Lawmakers should mandate the collection of comprehensive national statistics on police use of force. It’s astounding that this isn’t taking place. Congress also could encourage states to take decisions on prosecuting police officers accused of improper use of force out of local hands when appropriate.

The federal government can’t solve police departments’ problems for them, and even well-run departments will make mistakes. But, as the task force’s report put it, Washington can encourage police to “embrace a guardian — rather than a warrior — mindset.”